Expression of isolated DNA sequences in a plant host is dependent upon the presence of operably linked regulatory elements that are functional within the plant host. Choice of the regulatory sequences will determine when and where within the organism the isolated DNA sequence is expressed. Where continuous expression is desired throughout the cells of a plant, constitutive promoters are utilized. In contrast, where gene expression in response to a stimulus is desired, inducible promoters are the regulatory element of choice. Where expression in specific tissues or organs are desired, tissue-preferred promoters and/or terminators are used. That is, these regulatory elements can drive expression in specific tissues or organs. Additional regulatory sequences upstream and/or downstream from the core sequences can be included in expression cassettes of transformation vectors to bring about varying levels of expression of isolated nucleotide sequences in a transgenic plant.
Seed development involves embryogenesis and maturation events as well as physiological adaptation processes that occur within the seed to insure progeny survival. Developing plant seeds accumulate and store carbohydrate, lipid, and protein that are subsequently used during germination. Expression of storage protein genes in seeds occurs primarily in the embryonic axis and cotyledons and in the endosperm of developing seeds but never in mature vegetative tissues. Generally, the expression patterns of seed proteins are highly regulated. This regulation includes spatial and temporal regulation during seed development. A variety of proteins accumulate and decay during embryogenesis and seed development and provide an excellent system for investigating different aspects of gene regulation as well as for providing regulatory sequences for use in genetic manipulation of plants.
Isolation and characterization of seed-preferred promoters and terminators that can serve as regulatory elements for expression of isolated nucleotide sequences of interest in a seed-preferred manner are needed for improving seed traits in plants.